1. Field of the Invention
This invention relates to the magnetic recording art and more particularly, to magnetic recording media comprising a specific type of organosilicone compound as a lubricant.
2. Description of the Prior Art
Home video tape recorders have recently become popular, and portable types of small-size video tape recorders are now increasing in number. Video tape recorders of the type having a built-in video camera therein have been developed and are now commercially sold. These video tape recorders require improvements of magnetic recording media not only in recording density, but also in surface smoothness and travelling performance. This is because recording and reproducing systems for use in these video tape recorders are the so-called helical capstan systems using rotary magnetic heads and are provided with a mechanism for reproducing a still reproduction picture. Magnetic recording media such as a magnetic tape, which are used in the above type of recording and reproducing apparatus, are travelled while contacting the magnetic heads, guide pins, and the like. Hence, the magnetic layer of the recording medium should have a low coefficient of friction to ensure a stable travelling performance. Additionally, because the magnetic layer tightly contacts the rotary magnetic heads at the time of recording and reproducing operations, it is required to have good abrasion resistance. With small-size, portable video tape recorders, they are frequently used under severe outdoor conditions which involve either high temperature and high humidity conditions, or low temperature conditions. Even under these conditions, magnetic recording tapes have to be stably travelled.
In order to improve the characteristics such that the magnetic layer of magnetic recording media has a small coefficient of kinetic friction, a stable travelling performance, and a good abrasion resistance, there has been proposed use of a number of lubricants. For instance, there are added to a magnetic layer silicone oils such as dimethyl silicone, and fatty acid-modified organosilicone compounds of the following general formulas (I) (Japanese Laid-open Application No. 52-70811), (II) (Japanese Japanese Laid-open Application No. 57-12414), (III) (Japanese Laid-open Application No. 52-108804), and (IV) (Japanese Laid-open Application No. 57-12420). ##STR2##
However, silicone oils such as dimethyl silicone are not favorable. Although excellent in lubricating property, they have poor miscibility with binders in the magnetic layer and are apt to exude on the surface of the magnetic layer, thus causing the surface to become sticky and lowering electromagnetic conversion characteristics such as as S/N ratio.
The fatty acid-modified organosilicone compounds of the general formulas (I) through (IV) have, respectively, the following defects. The compounds of the general formula (I) have a good lubricating property and the compounds of the general formula (II) are stable and do not decompose even under high temperature and high humidity conditions. However, the compounds of the formulas (I) and (II) are not satisfactory in compatibility with binders and a magnetic layer containing the compounds is poor in durability when travelled over a long term. The compounds of the general formulas (III) and (IV) are more compatible with binders than the compounds of the formulas (I) and (II). However, the compounds of the formula (III) are disadvantageous in that they are poor in stability, cause a magnetic paint to gel, or adversely affect the dispersion of a magnetic paint. In addition, when a magnetic recording tape using a compound of the formula (III) is used for recording and reproducing purposes under high temperature and high humidity conditions, a stable travelling operation is not ensured. The compounds of the general formula (IV) do not show good lubricating and durability properties.